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THE ••BfcAST FURNACE.            :          .                 57
reactions, since there may.be present FeaOg, Fe304J FeO, Fer;GQ .and C02,   Two reactions occurring are (13) and (14),   : . :
..;   .              (13) 2
\'                   (14) 2 Fe+3;C02— Fe208+3 CO,                       ,::
the first, creating heat, and the second absorbing energy. . Experiments on carbon deposition were carried on by. Laudig.* He. passed blast-furnace gas over different ores, the gas contain^ ing about 7.5 per cent. C02, and 29 per cent. CO, the temperature being just above the melting point of zinc. The following list shows the results obtained, the figures being the weight of carbon deposited in per cent, of the weight of ore :
Min.              Max.
Old range soft hematites. ...... ..... 4.48              35.13
hard hematites .. . > . .... . . 2.16              12.88
blue ores .......... ..... 1.56     -          4.72
brown ores ............ .. 0.98         ,     24.92
magnetites .......... ; . . .nil                  nil         :
Mesabis . ............. . ..... _______ 10.20              36.40
Scale and cinder. , ..... ..:..;,...... 0.08    .           0.74
;    It was assumed by Laudig that the reducibility and value of an ore depended upon two 'conditions :
(1) That it should be of such a character that, carbon would be deposited throughout the mass;
,  (2) That it should 'not be too readily disintegrated or too much increased, in volume by this action.
Cases were cited in tests of some of the Mesabi ores where the mass increased to iour oi> five times its volume after exposure to the gas, thus explaining the choking and scaffolding encountered jWheh smelting. these fine varieties.
The reducibility of different ores was investigated by ^iborghjT ?who concludes that it is dependent upon the density of the ore as measured by the specific gravity. .Anything which increases1, the porosity assists the . reduction, as, for. instance, the roasting o:Ta carbonate or a hydrate. By the same reasoning, hematite wbiild be
'    *2Yans.'il. I.Jf.'JB.,Vol. XXVI, p. 269.     Werukmtorets Annaler, Vol. Lit, pp. 280-310.